Transconductor system for a power supply system

ABSTRACT

One example includes a transconductor system. The system includes a first transconductance amplifier that generates a control current in response to a first input voltage. The system also includes a second transconductance amplifier that generates an output signal in response to a second input voltage. The system further includes an intermediate amplifier that generates a control voltage in response to the control current and a third input voltage. The control voltage can be provided to the first and second transconductance amplifiers to set a transconductance of each of the first and second transconductance amplifiers to be approximately equal.

CROSS REFERENCE TO RELATED APPLICATIONS

Under 35 U.S.C. § 120, this continuation application claims benefits ofand priority to U.S. patent application Ser. No. 16/228,926, filed onDec. 21, 2018, now U.S. Pat. No. 10,432,157, issued Oct. 1, 2019, whichis a continuation application of U.S. patent application Ser. No.15/808,002, filed on Nov. 9, 2017, now U.S. Pat. No. 10,199,999, issuedFeb. 5, 2019, the entirety of which are hereby incorporated herein byreference.

TECHNICAL FIELD

This disclosure relates generally to electronic systems, and morespecifically to a transconductor system.

BACKGROUND

A transconductor (e.g., transconductance amplifier) is a circuit devicethat converts an input signal (e.g., an input voltage) to an outputsignal (e.g., an output current). A transconductor can have atransconductance that defines a gain of the transconductor, such thatthe transconductance can define an amplitude of the output signal inresponse to the input signal. Transconductors can be implemented in avariety of circuit applications, such as in power supply systems. Forexample, a given power supply system can generate an output voltagebased on an input voltage, with both the input and output voltages beingpotentially highly variable. For a buck converter, as an example, theinput voltage can be greater than the output voltage. The power supplysystem can include an input-current control loop and a differentialcurrent balancing loop (e.g., dual-phase) that can exhibit a loop gainthat can have a dependence on the input voltage and/or the outputvoltage. The loop gain can also be affected by a response time, such asin response to transient changes to the input voltage and/or the outputvoltage, and can also be affected by a bandwidth of the respectiveamplitudes of the input voltage and/or the output voltage.

SUMMARY

One example includes a transconductor system. The system includes afirst transconductance amplifier that generates a control current inresponse to a first input voltage. The system also includes a secondtransconductance amplifier that generates an output signal in responseto a second input voltage. The system further includes an intermediateamplifier that generates a control voltage in response to the controlcurrent and a third input voltage. The control voltage can be providedto the first and second transconductance amplifiers to set atransconductance of each of the first and second transconductanceamplifiers to be approximately equal.

Another example includes a transconductor system. The system includes afirst transconductance amplifier that generates a control current inresponse to a first input voltage and a second transconductanceamplifier that generates an output signal in response to a second inputvoltage. The system also includes an intermediate amplifier thatgenerates a control voltage in response to the control current and athird input voltage. The control voltage can be provided to the firstand second transconductance amplifiers to set a transconductance of thetransconductor system to be proportional to a ratio of the third inputvoltage and the first input voltage.

Another example includes a power regulator system. The system includes arectifier that converts an AC input voltage to an input voltage and abuck regulator that generates an output voltage in response to a powerregulation signal. The system further includes a transconductor systemthat generates the regulation signal in response to the input voltageand the output voltage. The transconductor system can have atransconductance that is proportional to a ratio of the input voltageand the output voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a transconductor system.

FIG. 2 illustrates an example of a power supply system.

FIG. 3 illustrates an example of a transconductor circuit.

DETAILED DESCRIPTION

This disclosure relates generally to electronic systems, and morespecifically to a transconductor system. The transconductor system canbe configured to generate an output signal in response to a set of inputsignals. The transconductor system can include a first transconductanceamplifier that is configured to generate a control current in responseto a first input voltage. As an example, the first input voltage cancorrespond to an output voltage that is provided from a buck converterin a power supply system that includes the transconductor. The outputvoltage can thus be provided to the first transconductance amplifier viaa voltage divider to provide a pair of inputs to the firsttransconductance amplifier. The transconductor system can also include asecond transconductance amplifier that is configured to generate anoutput signal in response to a second input voltage. As an example, thesecond input voltage can correspond to a current monitoring voltagecorresponding to an amplitude of an input current associated with aninput voltage that is provided to the power supply system that includesthe transconductor, such as from a rectifier. The current monitoringvoltage can thus be provided to the second transconductance amplifieralong with a predetermined reference voltage corresponding to a currentamplitude to which the amplitude of the input current is desired to beregulated.

The transconductor system further includes an intermediate amplifierthat can correspond to a voltage amplifier that is configured togenerate a control voltage in response to the control current and athird input voltage. As an example, the third input voltage cancorrespond to the input voltage that is provided to the power supplysystem. The control voltage can thus be provided to each of the firstand second transconductance amplifiers to control a transconductance ofeach of the first and second transconductance amplifiers. As an example,the first and second transconductance amplifiers can be fabricated fromfabrication-matched components (e.g., with respect to associatedtransistors), such that the control voltage can set the transconductanceof the first and second transconductance amplifiers to be approximatelyequal. The second transconductance amplifier can generate a regulationoutput signal that can be provided to a power regulator (e.g., a buckregulator), such that the transconductor system can have atransconductance that is proportional to a ratio of the input voltage(e.g., the third input voltage) and the output voltage (e.g., the firstinput voltage) to regulate the amplitude of the input current.Accordingly, the control loop of the power regulator system, having aloop gain that is proportional to a ratio of the output voltage and theinput voltage, can be controlled via the transconductor system, having atransconductance that is proportional to a ratio of the input voltageand the output voltage, to provide power regulation that is absent adependence on the amplitude of the input voltage or the output voltage.

FIG. 1 illustrates an example of a transconductor system 10. Thetransconductor system 10 can be implemented in any of a variety ofcircuit applications that require converting a voltage to an outputsignal, such as an output current. In the example of FIG. 1, thetransconductor system 10 generates a regulation output signal, which isdemonstrated as a current I_(REG) which can create a voltage V_(REG). Asan example, the transconductor system 10 can be implemented in a powersupply system (e.g., a buck power supply system), such as for charging abattery of an electronic device.

The transconductor system 10 includes a first transconductance amplifier12, a second transconductance amplifier 14, and an intermediateamplifier 16. The first transconductance amplifier 12 is configured togenerate a control current I_(CTRL) in response to a first input voltageV₁. As an example, the first input voltage V₁ can correspond to anoutput voltage that is provided from a buck converter in a power supplysystem that includes the transconductor system 10. For example, thefirst input voltage V₁ can be provided to the first transconductanceamplifier 12 via a voltage divider (not shown) to provide twoproportional voltages that are associated with the first input voltageV₁.

The second transconductance amplifier 14 is configured to generate thecurrent I_(REG) in response to a second input voltage V₂, and inresponse to the predetermined reference voltage V_(REF). As an example,the second input voltage V₂ can correspond to a current monitoringvoltage associated with an amplitude of a current associated with athird input voltage V₃ that can correspond to an input voltage that isprovided to the associated power supply system (e.g., from a rectifier).The predetermined reference voltage V_(REF) can correspond to a currentamplitude to which the amplitude of the input current (e.g., of thethird input voltage V₃) is desired to be regulated. Therefore, thesecond transconductance amplifier 14 can generate the current I_(REG)which can create the voltage V_(REG) based on an amplitude differencebetween the second input voltage V₂ and the predetermined referencevoltage V_(REF).

The intermediate amplifier 16 can be configured as a voltage amplifierthat is configured to generate a control voltage V_(CTRL) in response tothe control current I_(CTRL) and in response to the third input voltageV₃ that can correspond to the input voltage of the associated powersupply system. In the example of FIG. 1, the control voltage V_(CTRL) isprovided to each of the first and second transconductance amplifiers 12and 14 to control a respective transconductance of each of the first andsecond transconductance amplifiers 12 and 14. As an example, the firstand second transconductance amplifiers 12 and 14 can be fabricated fromrespective fabrication-matched components (e.g., with respect toassociated transistors, such as including differential pairs), such thatthe control voltage V_(CTRL) can set the transconductance of the firstand second transconductance amplifiers 12 and 14 to be approximatelyequal. For example, the first transconductance amplifier 12 and theintermediate amplifier 16 can be configured in a feedback arrangement,such that the amplitude of the control voltage V_(CTRL) is adjusted toregulate the control current I_(CTRL) relative to the third inputvoltage V₃. The adjustment of the control voltage V_(CTRL) can thus setthe transconductance of the second transconductance amplifier 14 to beapproximately equal to the first transconductance amplifier 12, suchthat the second transconductance amplifier 14 can generate the voltageV_(REG) based on the second input voltage V₂ relative to thepredetermined reference voltage V_(REF) and based on thetransconductance of the first and second transconductance amplifiers 12and 14.

Based on the operation of the transconductor system 10, thetransconductor system 10 can have a transconductance that isproportional to a ratio of the first input voltage V₁ and the thirdinput voltage V₃. As described previously, the power regulation voltageV_(REG) that can be provided to a power regulator (e.g., a buckregulator) that can have a control loop that is proportional to a ratioof an output voltage and an input voltage. By providing the third inputvoltage V₃ as the input voltage from the buck power regulator, and byproviding the first input voltage V₁ as the output voltage that isprovided to the power regulator system (e.g., from a rectifier), thecontrol loop of the power regulator system can provide power regulationthat is absent a dependence on the amplitude of the input voltage or theoutput voltage of the power regulation system, as described herein.

FIG. 2 illustrates an example of a power supply system 50. The powersupply system 50 can correspond to an AC-DC power supply system that isconfigured to convert an AC power voltage, demonstrated in the exampleof FIG. 2 as a voltage V_(AC), into a DC power voltage, demonstrated inthe example of FIG. 2 as an output voltage V_(OUT). As an example, thepower supply system 50 can be implemented in a charging circuit forcharging a battery of a portable electronic device.

The power supply system 50 includes a rectifier 52 that is configured torectify the AC input voltage V_(AC) to generate a DC input voltageV_(IN) (hereinafter “input voltage V_(IN)”) having an input currentI_(IN). The rectifier 52 can also include a number of other powerconditioning functions (e.g., filtering and/or step-down amplification)in addition to rectifying the AC input voltage V_(AC) to generate theinput voltage V_(IN). The input voltage V_(IN) is provided to atransconductor system 54 and to a current monitor 56. As an example, thecurrent monitor 56 is configured to monitor an amplitude of the inputcurrent I_(IN), and is thus configured to generate a monitoring voltageV_(CM) that is provided to the transconductor system 54. The currentmonitoring voltage V_(CM) can thus have an amplitude that isproportional to the input current I_(IN).

The power supply system 50 further includes a buck converter 58 that isconfigured to generate an output voltage V_(OUT) based on a powerregulation voltage V_(REG) that is generated by the transconductorsystem 54. The buck converter 58 can be configured as any of a varietyof switching buck converters that is configured to provide the outputvoltage V_(OUT) as a DC voltage at a lesser amplitude than the powerregulation voltage V_(REG). The output voltage V_(OUT) is provided tothe transconductor system 54 in a feedback manner, as described ingreater detail herein.

The transconductor system 54 can be configured to regulate a currentassociated with the input voltage V_(IN) based on providing the powerregulation voltage V_(REG). As an example, the transconductor system 54can be configured substantially similar to the transconductor system 10in the example of FIG. 1. For example, the first input voltage V₁ of thetransconductor system 10 can correspond to the output voltage V_(OUT) inthe example of FIG. 2, and the third input voltage V₃ of thetransconductor system 10 can correspond to the input voltage V_(IN) inthe example of FIG. 2. Therefore, the transconductor system 54 can beconfigured to provide the power regulation voltage V_(REG) at atransconductance that is proportional to a ratio of the input voltageV_(IN) and the output voltage V_(OUT). Additionally, the second inputvoltage V₂ of the transconductor system 10 can correspond to themonitoring voltage V_(CM), such that the transconductance can be set toprovide the power regulation voltage V_(REG) based on the amplitude ofthe current I_(IN) based on the predetermined reference voltage V_(REF),as described previously.

FIG. 3 illustrates an example of a transconductor circuit 100. Thetransconductor circuit 100 can be implemented in any of a variety ofcircuit applications that require converting a voltage to an outputsignal. In the example of FIG. 3, the transconductor circuit 100generates a pair of regulation output currents I_(REG1) and I_(REG2)that can be converted to voltages V_(REG1) and V_(REG2) as adifferential output signal. The transconductor circuit 100 cancorrespond to the transconductor system 54 in the example of FIG. 2.Therefore, reference is to be made to the example of FIG. 2 in thefollowing description of the example of FIG. 3.

The transconductor circuit 100 includes a first transconductanceamplifier 102, a second transconductance amplifier 104, and anintermediate amplifier 106. The first transconductance amplifier 102 isconfigured to generate a control current I_(CTRL) in response to theoutput voltage V_(OUT). In the example of FIG. 3, the output voltageV_(OUT) is provided to a voltage-divider formed by a set of resistorsR₁, R₂, and R₃. The voltage-divider provides a first divided voltageV_(OUT1) between the resistors R₁ and R₂ and a second divided voltageV_(OUT2) between the resistors R₂ and R₃, with the resistor R₃ beingcoupled to a low-voltage rail (e.g., ground). The first divided voltageV_(OUT1) is provided to a gate of a P-channel metal-oxide semiconductorfield-effect transistor (MOSFET, hereinafter “P-FET”) P₁, and the seconddivided voltage V_(OUT2) is provided to a gate of a P-FET P₂. The P-FETsP₁ and P₂ are arranged as a differential pair having a common sourceconnection, with the P-FET P₁ being coupled to a diode-connected N-FETN₁ and the P-FET P₂ being coupled to an N-FET N₂ that has a common gatecoupling to the N-FET N₁. The N-FETs N₁ and N₂ are coupled at a sourceto the low-voltage rail, with the N-FET N₂ having an output node 107 atthe drain that provides the control current I_(CTRL). In addition, thefirst transconductance amplifier 102 includes a control P-FET P₃ thatinterconnects the common source of the P-FETs P₁ and P₂ and a high railvoltage V_(DD). As described in greater detail herein, the control P-FETP₃ is controlled to conduct a tail current I_(GM1) that sets atransconductance of the first transconductance amplifier 102.

Based on the arrangement of the first transconductance amplifier 102,the first transconductance amplifier 102 is configured to generate thecontrol current I_(CTRL) based on the amplitude of the output voltageV_(OUT) and based on a transconductance set by the tail current I_(GM1).Based on the voltage-divider formed by the resistors R₁, R₂, and R₃, thedivided voltages V_(OUT1) and V_(OUT2) each have an amplitude that isproportional to the amplitude of the output voltage V_(OUT).Additionally, the first transconductor 102 has a transconductance (gm)that is variable based on the amplitude of the tail current I_(GM1).Accordingly, the control current I_(CTRL) has an amplitude that is basedon the amplitude of the output voltage V_(OUT) and the transconductanceset by the tail current I_(GM1).

The second transconductance amplifier 104 is configured to generate theregulation current I_(REG1) and I_(REG2) (which can be used to generaterespective first and second regulation voltages V_(REG1) and V_(REG2))in response to the voltage W_(CM). In the example of FIG. 3, thepredetermined reference voltage V_(REF) is provided to a gate of a P-FETP₄, and the voltage V_(CM) is provided to a gate of a P-FET P₅. TheP-FETs P₄ and P₅ are arranged as a differential pair having a commonsource connection, with the P-FET P₄ being coupled to a current source108 that is interconnected by a first output node 110 on which the firstregulation current I_(REG1) (generating the first regulation voltageV_(REG1)) is provided, and the P-FET P₅ being coupled to a currentsource 112 that is interconnected by a second output node 114 on whichthe second regulation current I_(REG2) (generating the second regulationvoltage V_(REG2)) is provided. The current sources 108 and 112interconnect the first and second output nodes 110 and 114 to thelow-voltage rail. In addition, the second transconductance amplifier 104includes a control P-FET P₆ that interconnects the common source of theP-FETs P₄ and P₅ and the high rail voltage V_(DD). As described ingreater detail herein, the control P-FET P₆ is controlled to conduct atail current I_(GM2) that sets a transconductance of the secondtransconductance amplifier 104.

Based on the arrangement of the second transconductance amplifier 104,the second transconductance amplifier 104 is configured to generate thefirst and second regulation currents I_(REG1) and I_(REG2) (generatingthe respective regulation voltages V_(REG1) and V_(REG2)) based on theamplitude of the voltage W_(CM) relative to the predetermined referencevoltage V_(REF) and based on a transconductance set by the tail currentI_(GM2). As described previously, the predetermined reference voltageV_(REF) can correspond to a corresponding current amplitude to which thepower supply system regulates the current I_(IN), on which the amplitudeof the voltage W_(CM) is based. Additionally, the second transconductor104 has a transconductance (gm) that is variable based on the amplitudeof the tail current I_(GM2). Accordingly, each of the regulationvoltages V_(REG1) and V_(REG2) (e.g., the differential voltage V_(REG))has an amplitude that is based on the amplitude of the voltage W_(CM)relative to the predetermined reference voltage V_(REF) and thetransconductance set by the tail current I_(GM2).

As an example, the circuit components of the first and secondtransconductance amplifiers 102 and 104 can be fabrication matched. Asdescribed herein, the term “fabrication matched” with respect to thecircuit components can refer to circuit components that are fabricatedas approximately identical with respect to size and/or electricalcharacteristics, and can be fabricated on the same wafer or same part ofa wafer to provide for substantially similar fabrication, temperature,and tolerance characteristics and sensitivities. Therefore, the firstand second transconductance amplifiers 102 and 104 can exhibitsubstantially identical performance characteristics. In addition, theP-FETs P₃ and P₆ can likewise be fabrication matched, such that the tailcurrents I_(GM1) and I_(GM2) can be approximately equal. Accordingly,the first and second transconductance amplifiers 102 and 104 can becontrolled by approximately equal tail currents I_(GM1) and I_(GM2),respectively, to provide an approximately equal transconductance.

In the example of FIG. 3, the intermediate amplifier 106 is configuredas a voltage amplifier that is configured to generate a control voltageV_(CTRL) on a control node 116 that is provided to the gate of each ofthe P-FETs P₃ and P₆ to set an amplitude of the respective tail currentsI_(GM1) and I_(GM2). The intermediate amplifier 106 includes a firstN-FET N₃ and a second N-FET N₄ that are arranged as a differential pairhaving a common source connection that is coupled to a current source118 that provides the differential current to the low-voltage rail. TheN-FET N₃ is coupled to a diode-connected P-FET P₇ and the N-FET N₄ iscoupled to a P-FET P₈ that has a common gate coupling to the P-FET P₇.The P-FETs P₇ and P₈ are coupled at a source to the high rail voltageV_(DD), with the P-FET P₈ having a drain that is coupled to the node 116on which the control voltage V_(CTRL) is provided.

In the example of FIG. 3, the gate of the N-FET N₃ is coupled to theoutput node 107 on which the control current I_(CTRL) is provided, andis also coupled to a resistor R_(GM) that interconnects the output node107 and a node 120. The gate of the N-FET N₄ is coupled to a firstresistor R₄ and a second resistor R₅ that are arranged as avoltage-divider with respect to the input voltage V_(IN) to provide acurrent I₁ through the resistor R₄, such that the gate of the N-FET N₄is controlled by a voltage that is proportional to the input voltageV_(IN). The resistor R₅ is coupled to the node 120, such that the node120 interconnects the resistor R₅ and a diode D1 that has a cathodecoupled to the low-voltage rail. Therefore, the differential pair of theN-FETs N₃ and N₄ is controlled by the control current I_(CTRL) and theinput voltage V_(IN).

Particularly, in the example of FIG. 3, the control current I_(CTRL)sets a voltage amplitude at the gate of the N-FET N₃ via the resistorR_(GM), and the input voltage V_(IN) sets a proportional voltage at thegate of the N-FET N₄ relative to a voltage at the node 120 that is basedon the control current I_(CTRL). Thus, the N-FETs N₃ and N₄ are operatedas differential pair in the saturation mode of operation based on theinput voltage V_(IN) and the control current I_(CTRL). In response, theintermediate amplifier 106 operates to substantially equalize the gatevoltages of the N-FETs N₃ and N₄, and thus to equalize the current flowthrough each of the N-FETs N₃ and N₄. Therefore, the amplitude of thecontrol voltage V_(CTRL) is adjusted based on the gate voltagedifference between the N-FET N₃ and N-FET N₄ that results from theamplitude of the control current I_(CTRL), as provided by the voltage atthe node 120 across the resistor R_(GM). Accordingly, the controlvoltage V_(CTRL) adjusts the activation state of the P-FET P₃ to modifythe tail current I_(GM1), and thus the transconductance of the firsttransconductance amplifier 102, to modify the amplitude of the controlcurrent I_(CTRL) in a feedback manner. The change in the amplitude ofthe control current I_(CTRL) thus adjusts the differential control ofthe differential pair of the N-FETs N₃ and N₄ to provide a steady-stateof operation. Accordingly, the intermediate amplifier 106 and the firsttransconductance amplifier 102 are arranged in a feedback manner tomodify the transconductance of the first transconductance amplifier 102.

As described previously, the circuit components of the first and secondtransconductance amplifiers 102 and 104 can be fabrication matched, andthe P-FETs P₃ and P₆ can likewise be fabrication matched. As a result,the changes in amplitude of the control voltage V_(CTRL) to change theamplitude of the tail current I_(GM1) via the P-FET P₃ can likewisechange the amplitude of the tail current I_(GM2) via the P-FET P₆.Accordingly, the change to the transconductance of the firsttransconductance amplifier 102 via the amplitude of the control voltageV_(CTRL) can likewise result in an approximately identical change in thetransconductance of the second transconductance amplifier 104 via theamplitude of the control voltage V_(CTRL). Accordingly, the secondtransconductance amplifier 104 can provide the differential regulationvoltage V_(REG1) and V_(REG2) based on the voltage V_(CM) relative tothe predetermined reference voltage V_(REF) at approximately the sametransconductance as the first transconductance amplifier 102.

The operation of the transconductor circuit 100 can better be explainedmathematically. The transconductance GM₁ of the first transconductanceamplifier 102 can be expressed as follows:GM ₁ =I _(CTRL) /∝V _(OUT)   Equation 1

-   -   Where: ∝ V_(OUT) corresponds to the proportional relationship        between the voltages V_(OUT1) and V_(OUT2).        The control of the first N-FET N₃ of the intermediate amplifier        106 can thus be expressed as follows:        I _(CTRL) *R _(GM) =I ₁ *R ₅ =V _(IN)*(R ₅/(R ₄ +R ₅))          Equation 2        I _(CTRL) =V _(IN)*(R ₅/(R ₄ +R ₅))*(1/R _(GM))   Equation 3        Therefore, the transconductance GM₁ can be expressed as:        GM ₁=(V _(IN) /V _(OUT))*(R ₅/(R ₄ +R ₅))*(1/(∝R _(GM)))          Equation 4        Accordingly, as demonstrated in Equation 4, the transconductance        GM₁ is proportional to a ratio of the input voltage V_(IN) and        the output voltage V_(OUT). As described previously, the        transconductance GM₂ of the second transconductance amplifier        104 is approximately equal to the transconductance GM₁.        Accordingly, the transconductance GM₂ of the second        transconductance amplifier 104 can be expressed as:        GM ₂ =GM ₁=(V _(IN) /V _(OUT))*(R ₅/(R ₄ +R ₅))*(1/(∝R _(GM)))          Equation 5

As a result, the transconductor circuit 100 can exhibit atransconductance that is proportional to a ratio of the input voltageV_(IN) and the output voltage V_(OUT). As described previously, thepower regulation voltage V_(REG) that can be provided to the buckconverter 58 that can have a control loop that is proportional to aratio of the output voltage V_(OUT) and the input voltage V_(IN). Forexample, by implementing the transconductor circuit in the input currentregulation loop, the normal dependence on V_(OUT) and V_(IN) can beeliminated (e.g., V_(OUT)/V_(IN)*V_(IN)/V_(OUT)=1). Accordingly, thecontrol loop of the power regulator system 50 can provide powerregulation that is absent a dependence on the amplitude of the inputvoltage V_(IN) or the output voltage V_(OUT) of the power regulationsystem 50. This allows loop gain and bandwidth to be maximized, whichenhances the transient response time and mitigates potential overload onthe input source. The transconductor circuit 100 further helps simplifystabilizing the power regulator system loop 50 in the presence ofvarious critical frequencies.

What have been described above are examples of the present invention. Itis, of course, not possible to describe every conceivable combination ofcomponents or methodologies for purposes of describing the presentinvention, but one of ordinary skill in the art will recognize that manyfurther combinations and permutations of the present invention arepossible. Accordingly, the present invention is intended to embrace allsuch alterations, modifications and variations that fall within thespirit and scope of the appended claims. Additionally, where thedisclosure or claims recite “a,” “an,” “a first,” or “another” element,or the equivalent thereof, it should be interpreted to include one ormore than one such element, neither requiring nor excluding two or moresuch elements. As used herein, the term “includes” means includes butnot limited to, and the term “including” means including but not limitedto. The term “based on” means based at least in part on.

What is claimed is:
 1. A power supply circuit comprising: a firsttransconductance amplifier configured to generate a control currentamplified from a first voltage and based on a first transconductance; asecond transconductance amplifier configured to generate an outputsignal amplified from a second voltage and based on a secondtransconductance; an intermediate amplifier configured to generate acontrol voltage based on the control current and a third voltage, thecontrol voltage is received by the first and second transconductanceamplifiers to equalize the first transconductance and the secondtransconductance; and a buck converter having a voltage input terminalconfigured to receive the output signal, and a voltage output terminalconfigured to provide the first voltage.
 2. The power supply circuit ofclaim 1, in which: the first voltage is derived from an output voltage;the second voltage corresponds to an amplitude of an input current; andthe third voltage is derived from an input voltage.
 3. The power supplycircuit of claim 1, in which the first transconductance amplifier isconfigured to set the first transconductance, based on the controlvoltage, to a ratio of the third voltage over the first voltage.
 4. Thepower supply circuit of claim 1, in which the second transconductanceamplifier is configured to set the second transconductance, based on thecontrol voltage, to a ratio of the third voltage over the first voltage.5. The power supply circuit of claim 1, including: an input terminalcoupled to the intermediate amplifier to provide the third voltage; acurrent monitor circuit having an input coupled to the input terminal,and an output coupled to the second transconductance amplifier toprovide the second voltage; and a buck converter having an input coupledto the second transconductance amplifier to receive the output signal,and an output fed back to the first transconductance amplifier toprovide the first voltage.
 6. The power supply circuit of claim 1, inwhich the first transconductance amplifier includes a differentialamplifier having: a first input coupled to receive a first portion ofthe first voltage; a second input coupled to receive a second portion ofthe first voltage; a controlled current source having a control terminalcoupled to receive the control voltage; and an output configured todeliver the control current.
 7. The power supply circuit of claim 6, inwhich the controlled current source is configured to adjust the firsttransconductance to approximate the second transconductance based on thecontrol voltage.
 8. The power supply circuit of claim 1, in which thesecond transconductance amplifier includes a differential amplifierhaving: a first input coupled to receive a reference voltage; a secondinput coupled to receive the second voltage; a controlled current sourcehaving a control terminal coupled to receive the control voltage; and anoutput configured to deliver the output signal.
 9. The power supplycircuit of claim 8, in which the controlled current source is configuredto adjust the second transconductance to approximate the firsttransconductance based on the control voltage.
 10. The power supplycircuit of claim 1, in which the intermediate amplifier includes: aconductive path to receive the control current; and a differentialamplifier having: a first input coupled to the conductive path; a secondinput coupled to receive a portion of the third voltage; and an outputconfigured to deliver the control voltage.
 11. A power supply circuitcomprising: a first transconductance amplifier configured to generate acontrol current amplified from an output voltage and based on a firsttransconductance; a second transconductance amplifier configured togenerate a regulation signal amplified from a sensed voltageproportional to an input current and based on a second transconductance;an intermediate amplifier configured to generate a control voltage basedon the control current and an input voltage; and a buck converter havinga voltage input terminal configured to receive the regulation signal,and a voltage output terminal configured to provide the output voltage,in which the first and second transconductance amplifiers are configuredto adjust the first and second transconductance based on the controlvoltage.
 12. The power supply circuit of claim 11, in which: the firsttransconductance amplifier includes a first controlled current sourceconfigured to adjust, based on the control voltage, the firsttransconductance to approximate the second transconductance; and thesecond transconductance amplifier includes a second controlled currentsource configured to adjust, based on the control voltage, the secondtransconductance to approximate the first transconductance.
 13. Thepower supply circuit of claim 11, in which the intermediate amplifierincludes: a conductive path to receive the control current; and adifferential amplifier having: a first input coupled to the conductivepath; a second input coupled to receive a portion of the input voltage;and an output configured to deliver the control voltage.
 14. The powersupply circuit of claim 11, in which the first transconductanceamplifier is configured to set the first transconductance to a ratio ofthe input voltage over the output voltage.
 15. The power supply circuitof claim 11, in which the second transconductance amplifier isconfigured to set the second transconductance to a ratio of the inputvoltage over the output voltage.
 16. A power supply circuit comprising:a first transconductance amplifier having a first controlled currentsource configured to adjust a first transconductance based on a controlvoltage, the first transconductance amplifier configured to generate acontrol current by amplifying an output voltage with the firsttransconductance; a second transconductance amplifier having a secondcontrolled current source configured to adjust a second transconductancebased on the control voltage, the second transconductance amplifierconfigured to generate a regulation signal by amplifying a sensedvoltage proportional to an input current with the secondtransconductance; an intermediate amplifier configured to generate thecontrol voltage based on the control current and an input voltage; and abuck converter having a voltage input terminal configured to receive theregulation signal, and a voltage output terminal configured to providethe output voltage.
 17. The power supply circuit of claim 16, including:an input terminal coupled to the intermediate amplifier to provide theinput voltage; a current monitor circuit having an input coupled to theinput terminal, and an output coupled to the second transconductanceamplifier to provide the sensed voltage; and a buck converter having aninput coupled to the second transconductance amplifier to receive theregulation signal, and an output fed back to the first transconductanceamplifier to provide the output voltage.
 18. The power supply circuit ofclaim 16, in which the first controlled current source is configured toadjust the first transconductance to a ratio of the input voltage overthe output voltage.
 19. The power supply circuit of claim 16, in whichthe second controlled current source is configured to adjust the secondtransconductance to a ratio of the input voltage over the outputvoltage.
 20. The power supply circuit of claim 16, in which theintermediate amplifier includes: a conductive path to receive thecontrol current; and a differential amplifier having: a first inputcoupled to the conductive path; a second input coupled to receive aportion of the input voltage; and an output configured to deliver thecontrol voltage.
 21. The power supply circuit of claim 1 including:rectifier circuitry having an alternating current voltage input and adirect current voltage output coupled to the third voltage of theintermediate amplifier; and current monitor circuitry having an inputcoupled to the direct current voltage output and having a currentmonitor voltage output coupled to the second voltage of the secondtransconductance amplifier.
 22. The power supply circuit of claim 11including: rectifier circuitry having an alternating current voltageinput and a direct current voltage output coupled to the input voltageof the intermediate amplifier; and current monitor circuitry having aninput coupled to the direct current voltage output and having a currentmonitor voltage output coupled to the sensed voltage of the secondtransconductance amplifier.
 23. The power supply circuit of claim 16including: rectifier circuitry having an alternating current voltageinput and a direct current voltage output coupled to the input voltageof the intermediate amplifier; and current monitor circuitry having aninput coupled to the direct current voltage output and having a currentmonitor voltage output coupled to the sensed voltage of the secondtransconductance amplifier.
 24. A power supply circuit having a highvoltage rail and a low voltage rail, comprising: a direct currentvoltage input; converter circuitry having a regulated voltage input anda voltage output; and a transconductor circuit including: a firsttransconductance amplifier having an input coupled to the voltageoutput, having a first control voltage input and having a controlcurrent output, the first transconductance amplifier having a firsttransconductance; a second transconductance amplifier having a referencevoltage input, having a current monitor voltage input coupled to thedirect current voltage input, having a second control voltage input, andhaving a regulated voltage output coupled to the regulated voltageinput, the second transconductance amplifier having a secondtransconductance; and an intermediate amplifier having an input coupledto the direct current voltage input, having an input coupled to thecontrol current output, and having a control voltage output coupled tothe first control voltage input and the second control voltage input.25. The power supply circuit of claim 24 in which the transconductancecircuit has a transconductance proportional to an input voltage on thedirect current voltage input and an output voltage on the voltageoutput.
 26. The power supply circuit of claim 24 in which the firsttransconductance amplifier and the second transconductance amplifierhave circuit components that are fabrication matched.
 27. The powersupply of claim 24 in which the control voltage output provides acontrol voltage to result in an approximately identical change in thefirst transconductance and the second transconductance.
 28. The powersupply circuit of claim 24 including a feedback loop between the firsttransconductance amplifier and the intermediate amplifier, the feedbackloop including the control current output and the control voltage input.29. The power supply of claim 24 in which the transconductor circuitincludes current monitor circuitry having an input coupled to the directcurrent voltage input and a current monitor voltage output coupled tothe current monitor voltage input.
 30. The power supply of claim 24 inwhich the first transconductance amplifier includes a first controltransistor and a first differential pair of transistors coupled betweenthe high voltage rail and the low voltage rail, the first controltransistor having a gate coupled to the first control voltage input, thefirst differential pair of transistors having a gate coupled to thevoltage output input and having a drain coupled to the control currentoutput.
 31. The power supply of claim 24 in which the secondtransconductance amplifier includes a second control transistor and asecond differential pair of transistors coupled between the high voltagerail and the low voltage rail, the second control transistor having agate coupled to the second control voltage input, the seconddifferential pair of transistors having a gate coupled to the referencevoltage input, having a gate coupled to the current monitor voltageinput, and having a drain coupled to the regulated voltage output. 32.The power supply of claim 31 in which the second differential pair oftransistors have drains coupled to differential first and secondregulated voltage outputs.
 33. The power supply of claim 24 in which theintermediate amplifier is a voltage amplifier having a pair of commongate connected transistors, a control voltage node, and a thirddifferential pair of transistors coupled between the high voltage railand the low voltage rail, the third differential pair of transistorshaving a gate coupled to the control current output, and the controlnode being coupled to the control voltage output.
 34. The power supplycircuit of claim 24 in which the converter circuitry is buck convertercircuitry.